1. Field of the Invention
The present invention relates to a light emission apparatus configured to emit a light beam, an optical scanning apparatus including the light emission apparatus, and an image forming apparatus including with the optical scanning apparatus.
2. Description of the Related Art
In an image forming apparatus such as an electrophotographic copying machine or printer, scanning is performed on a photosensitive member with a light beam such as a laser beam to form an electrostatic latent image on the photosensitive member, and the electrostatic latent image is developed with toner to form an image. A light emission apparatus such as an optical scanning apparatus is used as the apparatus for emitting the laser beam with which the photosensitive member is exposed.
In the above-mentioned optical scanning apparatus, light from a semiconductor laser serving as the light source is converted to substantially parallel light to be deflected by a rotating polygon mirror (hereinafter simply referred to as the polygon mirror). Scanning is performed on the photosensitive member in a substantially linear fashion with the laser beam deflected by the rotating polygon mirror.
To keep up with recent increasing demand in image forming speed and in image resolution, optical scanning apparatuses nowadays perform exposure on the photosensitive member with a plurality of laser beams emitted from a plurality of light emission points. In particular, a vertical cavity surface emitting laser (VCSEL) is adopted as the light source of an optical scanning apparatus since it allows easy arrangement of a large number of light emission points.
In an optical scanning apparatus, the optical path of the light beam emitted from the light source affects the laser beam configuration on the photosensitive member, the image forming position of the laser beam, and the light quantity, so that it is necessary to maintain a high installation precision for the light source components such as a lens and mirror. In the case where a VCSEL is used as the light source, exposure is performed on the photosensitive member with a laser beam passing the vicinity of the optical axis of the lens such as a collimator lens, and a laser beam passing portion separate from the optical axis of the lens.
Strictly speaking, the optical performance of the optical axis portion of a lens and the optical performance of a portion separate from the optical axis are different. The optical performance of a lens is the highest at the optical axis portion.
When the positional precision of the VCSEL is low, the positional relationship between the lens and the VCSEL is not ideal, so that the laser beam passes a position further separate from the optical axis of the lens than the position of the design value. Such a laser beam does not have desired characteristics in terms of the light quantity on the photosensitive member, spot configuration, etc., which may lead to deterioration in image quality. Thus, enhancement of the positional precision (installation precision) of the VCSEL is required.
Japanese Patent Application Laid-Open No. 2009-187028 discusses an optical scanning apparatus which provides on the upper surface of the package of a VCSEL a reference surface (contact portion) parallel to the flat surface on which the light emission points are placed, and which mounts on the board a connection member provided between an optical unit and a board on which the VCSEL package is disposed such that the connection member bends in the optical axis direction.
In the optical scanning apparatus discussed in Japanese Patent Application Laid-Open No. 2009-187028, the VCSEL package reference surface is brought into contact with the reference surface on the optical unit side by a restoring force generated in the connection member. Thus, high precision can be secured in terms of the verticality of the optical axis and the VCSEL package.
However, as illustrated in FIG. 10, in the light emission apparatus mounting structure discussed in Japanese Patent Application Laid-Open No. 2009-187028, a connection member 1002 connected to a laser holder bends a board 1003 in an archlike manner so as to make it convex on the side of the surface on which a VCSEL package 1004 is mounted. As a result, warpage is also generated in the board 1003 in the same direction and to the same degree, generating a great stress at a solder bonding portion for electrically connecting and holding the VCSEL package 1004 and the board 1003.